[dev.typeparams] cmd/compile: do transformCall with non-shape type of call

Do the transformCall using the original types2-derived type of the call
(in particular, the types of the params as non-shapes). Currently, since
we were using the param types of the instantiation, we might add in
interface conversions to an interface with shapes in the one case of a
full-instantiated generic call. So, we do the transformCall() before
installing the shaped-based instantiation. transformCall() works
correctly even in the case of OCALL/FUNCINST.

Fixed two related bugs:
  - Fixed case where we still were not correctly substituting the types
    for a function instantiation.
  - The type substituter needs to copy field flags while substituting in
    tstruct.

Change-Id: I14e960737d6840a75846ede480e6650534ba3af3
Reviewed-on: https://go-review.googlesource.com/c/go/+/340259
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/noder/expr.go b/src/cmd/compile/internal/noder/expr.go
index 6e2b1a839b..3e3c352a32 100644
--- a/src/cmd/compile/internal/noder/expr.go
+++ b/src/cmd/compile/internal/noder/expr.go
@@ -125,13 +125,17 @@ func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
 			}
 			if fun.Op() == ir.OFUNCINST {
 				// Replace explicit type args with the full list that
-				// includes the additional inferred type args
+				// includes the additional inferred type args.
+				// Substitute the type args for the type params in
+				// the generic function's type.
 				fun.(*ir.InstExpr).Targs = targs
+				newt := g.substType(fun.Type(), fun.Type().TParams(), targs)
+				typed(newt, fun)
 			} else {
 				// Create a function instantiation here, given there
 				// are only inferred type args (e.g. min(5,6), where
 				// min is a generic function). Substitute the type
-				// args for the type params in the uninstantiated function's
+				// args for the type params in the generic function's
 				// type.
 				inst := ir.NewInstExpr(pos, ir.OFUNCINST, fun, targs)
 				newt := g.substType(fun.Type(), fun.Type().TParams(), targs)